Disclosed in applicant's British Patent Application No. 2188199 is a polymer housed solid-state surge arrester which represents a considerable departure from conventional porcelain housed arresters and is finding substantial commercial success. This arrester, which was developed from the arrester that is disclosed in application British Patent No. 2073965, comprises an elongate core constituted, preferably, by a distributed array of zinc oxide varistor blocks and electrically-conductive heat sink/spacer blocks in face-to-face contact between first and second terminal blocks and with the said blocks encased within a rigid shell of reinforced rigid plastic material bonded to the peripheral surfaces of the blocks, and a shedded outer housing for said core comprising a sleeve of polymeric heat-shrink material or elastomeric material shrunk or released tightly onto said core with a weather-proof sealant between the core and the heat-shrink or elastomeric material or comprising in-situ molded synthetic plastic material. The heat sink/spacer blocks are not essential to the arrester of British Patent Application No. 2188199, but provide advantageous voltage grading and thermal distribution effects within the arrester and are preferred for this reason.
As described in GB 2188199, the surge arrester therein disclosed has very considerable physical strength since its construction is based upon a core formed of ceramic varistor blocks and metallic heat-sink/spacer blocks encased within a reinforced plastic shell which is bonded to the surfaces of the blocks. The varistor and heat-sink/spacer blocks can even be adhesively secured in face-to-face contact by use of electrically conductive adhesives, to adds to the physical strength of the core. Specifically mentioned in GB 2188199 is an improvement which can be obtained in the dressing of power distribution poles by virtue of using surge arresters of the construction therein described; by virtue of the great physical strength of the surge arresters per se, stand-off support insulators, which were previously required to ensure that the conventional porcelain arrester was not physically loaded, can be dispensed with, leading to a more cost effective, more readily installed, and aesthetically and environmentally more acceptable installation.
The polymeric surge arrester disclosed in GB 2188199 is inherently well adapted to utilization as a distribution class arrester, and the available sizes of varistor blocks and other limitations have dictated the continued utilization of large size porcelain housed arresters for station class and other high voltage applications. Such large porcelain arresters, wherein the arrester components are sealed within a shedded porcelain housing commonly with an inert gas filling and with elaborate blow-out mechanisms provided to protect the arrester against explosive destruction, are disadvantageous for a variety of reasons. They namely they are expensive to manufacture and test; they are difficult to transport to their utilization site and are prone to damage both during transportation and subsequent erection; they are difficult to install and require the use of heavy lifting equipment; and they are inherently liable to the type of electrical problems that the polymeric arrester of GB 2188199 avoids (e.g., internal ionization leading to degradation of internal components).